Effect of the passive films on CaCO3 scale depositing on Q235 steel: Electrochemical and surface investigation

The deposition of the CaCO3 scale in circulating cooling water is a common and serious concern in the industry, which hinders the heat transfer, reduces water flow and blocks membrane filters. This paper aims at studying the effect of the gamma-Fe2O3, Fe-2(MoO4)(3)center dot Fe2O3 and FePO4 center dot gamma-Fe2O3 passive films on CaCO3 scale deposition on Q235 steel by electrochemical methods, including linear sweep voltammetry (LSV), chronoamperometry and electrochemical impedance spectroscopy (EIS) tests. The scale and corrosion inhibition performance of the passive films was evaluated by the residual current density (i(r)) and charge transfer resistance (R-ct) values. Electrochemical results suggested that the passive films could inhibit corrosion and reduce the CaCO3 scale deposition on Q235 steel and the FePO4 center dot gamma-Fe2O3 complex passive film showed the best anti-scaling effect. Scanning electron microscope (SEM) and X-ray diffractometer (XRD) tests showed that the passive films could lead to a decrease in the proportion of aragonite to calcite under cathodic water reduction conditions and the composition of the FePO4 center dot gamma-Fe2O3 complex passive film could deform the CaCO3 crystal. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

This study investigated the effect of different passive films on CaCO3 scale deposition on Q235 steel and evaluated their corrosion inhibition and scaling inhibition performance. The results showed that the FePO4 center dot γ-Fe2O3 complex passive film exhibited the best anti-scaling effect.